Macbeth was completely shocked at this. Macbeth was confused at how he could be Thane of Cawdor when there was already one. He didn't believe them at first. It only took one truth in all of these falsehoods. Little did Macbeth know that he was already Thane of Cawdor even before the witches predictions. "No more that Thane of Cawdor shall deceive our bosom interest: go pronounce his present death, and with his former title greet Macbeth." (Act 1 Scene 1 Lines 63-65)
Soon after that the king's servant Ross and Lennox brought the news to Macbeth and Banquo just after the predictions from the weird sisters. He even was wary of what the messengers had to say to him. "The Thane of Cawdor lives: why do you dress me in borrowed robes?" (Act I Scene 3 Line 109)
Finally after messengers had convinced Macbeth they were not telling him falsehoods, he took faith in what they had told him. This brought him to realize that the three witches told the truth. He believed what these strange women told him, taking it as truth instead of shrugging off his shoulders like Banquo did. Because of